As sys or system
create public database link link_name using 'tns_entry_name';
As the user using the link
create database link public_link_name connect to remote_db_username identified by remote_db_pw;
There are two types of researchers. Those who have done something and those who haven't. The latter will say there are 143 ways to do something, and the former will say 142 of them don't work. - Quote from a System V researcher